High-voltage outdoor vaccum switch with conductive coating serving as electrostatic shield means and end cap-mounting means

ABSTRACT

A high-voltage vacuum switch for outdoor use comprises a hollow cylindrical skirted ceramic envelope having electrically conductive coatings on the inner and outer surfaces at each end. End cap assemblies are provided at each end and each assembly comprises a ring of material thermally compatible with the envelope, which is brazed to a metal coating, fused to the ceramic and the other end of the ring welded to a collar forming part of an end cap assembly. In one end cap assembly, the collar is brazed or welded to a plate which is brazed to a stationary contact stud, having a disc-type arc shield attached thereon, which extends into the envelope. In the other end cap assembly, the collar is brazed or welded to a plate having a hole which accommodates a movable contact stud. A bellows is brazed or welded between the plate of the said end cap assembly and a washer attached to the movable contact stud. A cylindrical arc shield is brazed or welded to the plate and a disc-type arc shield is brazed or welded inside the cylindrical arc shield Both end cap assemblies are provided electrical and mechanical connection means.

United States Patent [72] Inventors Zygmunt A. Wach'ta 3,189,715 6/1965Jennings ZOO/144.2

Boston; 3,355,564 11/1967 Ranheim 200/1442 Oscar L. Larkin, Saugus, bothof, Mass. 3,440,377 4/1969 Wesoloski ZOO/144.02 [2U P 782373 PrimaryExaminer-Robert K. Schaefer [22] Filed Dec. 9, 1968 AssistantExaminer-Robert A. Vanderhye [45] Patented June 1971 Attorneys- ThomasF. Kirby Robert B. Benson and Lee H [73] Assignee Allis-ChalmersManufacturing Company Kai ser Milwaukee, Wis.

[54] HIGHNOLTAGE OUTDOOR VACUUM SWITCH ABSTRACT: A high-voltage vacuumswitch for outdoor use WITH CONDUCTIVE COATING SERVING AS ELECTROSTATICSHIELD MEANS AND END CAP- comprises a hollow cylindrical skirted ceramicenvelope having electrically conductive coatings on the inner and outersurfaces at each end. End cap assemblies are provided at each end andeach assembly comprises a ring of material thermally compatible with theenvelope, which is brazed to a metal coating, fused to the ceramic andthe other end of the ring welded to a collar forming part of an end capassembly. In one end cap assembly, the collar is brazed or welded to aplate which is brazed to a stationary contact stud, having a disc-typearc shield attached thereon, which extends into the envelope. In theother end cap assembly, the collar is brazed or welded to a plate havinga hole which accommodates a movable contact stud. A bellows is brazed orwelded between the plate of the said end cap assembly and a washerattached to the movable contact stud. A cylindrical arc shield is brazedor welded to the plate and a disc-type arc shield is brazed or weldedinside the cylindrical arc shield Both end cap assemblies are providedelectrical and mechanical connection means.

HIGH-VOLTAGE OUTDOOR VACUUM SWIITQllii Wll'llllll CONDUCTIVE COATllNGSERVING AS ELECTROSTATIC SHIELD MEANS AND END CAP-MOUNTKNG MEANS SUMMARYOF THE INVENTION This invention relates to vacuum-type electricaldevices, such as high-voltage vacuum interrupters, switches and circuitbreakers, which are primarily adapted for outdoor use.

Present devices of the foregoing type are quite fragile and not suitedfor outdoor use unless physically protected by plastic, ceramic orinsulated metal enclosures. Furthermore, present devices are soconstructed that voltage gradients occur at the ends thereof to causecorona discharge unless special measures are taken. Also, fabricationtechniques presently employed tend to preclude the use of standardizedelectrical terminations and mounting means for such devices. Finally,these same fabrication techniques and material selections dictate adevice which has many components which are not easily standardized forrapid and simple assembly.

It is desirable, therefore, to provide improved vacuum-type electricaldevices, such as vacuum interrupters and the like, which overcome theaforesaid drawbacks and have other advantages.

A vacuum-type electrical device in accordance with the present inventioncomprises a hollow tubular insulating envelope, exteriorly skirted toincrease electrical creepage distance. The envelope ends are provided ontheir exterior and interior surfaces with electrostatic shield meanswhich control voltage gradients and serve as a means whereby end capassemblies can be vacuum sealed to the envelope. Each end cap assemblycomprises an electrically conductive ring which is electrically andmechanically connected to the elec trostatic shield means. Each ring hasthermal expansion characteristics which are similar to those of theenvelope. Each end cap assembly comprises a collar which is electricallyand mechanically connected to its respective ring. Each end cap assemblyfurther comprises an end plate which is electrically and mechanicallyconnected to its respective collar and also affords mechanical supportfor one or more electrical components such as contact studs, bellows,and arc shields which are housed within the envelope. The various partsin the end cap assemblies and their associated components are sofabricated and machined so as to be interfitting, self-aligning andsubject to a minimum number of brazing and/or welding steps.

It is an object of the present invention to provide improved vacuum-typeelectrical devices.

Another object is to provide improved vacuum-type electrical devicessuch as vacuum interrupters, switches and circuit breakers primarily foroutdoor use.

Another object is to provide devices of the aforesaid character whichare electrically reliable, physically rugged, usable outdoors withoutadditional protective means or spe cial adapters, and in which voltagegradients at the ends thereof are substantially eliminated therebyavoiding the need for corona shields or the need for excessive flashoverdistance between end rings by virtue of the resultant increased coronathreshold voltages achieved.

Another object is to provide devices of the aforesaid character whichemploy improved and simplified manufacturing and assembly techniques andthe latest technology.

Another object is to provide devices of the aforesaid character whichhave fewer parts, increased strength, are more easily standardized, andlend themselves to higher tem' perature bake-out and welding processesduring manufacture to thereby enhance overall performance.

Otln-r obj c' s and advantages of the invention will hereinafter appear.

DESCRIPTION OF THE DRAWINGS The accompanying drawing illustrates apreferred embodiment of the invention, but it is to be understood thatthe embodiment illustrated is susceptible of modifications with respectto details thereof without departing from the scope of the appendedclaims.

In the drawing, the single FIGURE shows a side elevationalcross-sectional view of a vacuum interrupter in accordance with thepresent invention.

DESCRIPTION OF THE INVENTION Referring to the drawing, the numeral 10designates a vacuum-type electrical device such as a high-voltage vacuuminterrupter or vacuum switch in accordance with the present inventionand particularly well suited for outdoor use. Device 10 comprises ahollow cylindrical or tubular open ended envelope 12 which is made ofnonporous insulating material which has great physical strength and iswell adapted to have other material hermetically sealed thereto. Inpractice, envelope 1.2 is preferably made of high-density nonporousvacuum grade ceramic such as alumina either with enough silica thereinfor fusion to a metallic surface deposit or with silicon based adductsto the metallic deposit. Envelope 12 is preferably glazed on itsexterior. Envelope 12 is provided on its exterior with a plurality ofskirts, corrugations or sheds 14 which are of such number and dimensionto provide a lengthwise creepage ratio of about L5 to 1 or greater.

Electrostatic shielding means 1.6 and 18 are provided at opposite endsof envelope 12 to reduce or eliminate voltage gradients which wouldotherwise occur and provide corona discharge in high-voltage outdoor useof device 10. Shielding means 16 and 18 are substantially identical inform and function and, therefore, only the former will be described indetail. Shielding means 16 comprise a continuous electrically conductivemember which extends on the inside surface of envelope 12 as far in asthe thickest portion of the first skirt 14 of the envelope, and teaposition closer to the opposite electrode 78 than any external edge 29of the end cap. The position of the internal edge of shielding means 16causes a concentration of voltage gradients thereon. Voltage gradientsso disposed in vacua will not cause corona because of the absence of anygaseous media necessary for this phenomenon. Shielding means 16 alsocover the extreme end surface of envelope 12 and extend on the outsidesurface of the envelope as far as is practical to the base of the firstskirt 14. Preferably, shielding means 16 takes the form of anelectrically conductive coating which is applied by brush, spray or dipand firmly adheres to envelope 12. In practice, a coating comprising amolybdenum-manganese alloy fired at a temperature sufficient to causefusion sintering thereof to the silica in envelope I2 and then providedwith a nickel plate by electrolysis or chemical bath gives good results.If preferred, however, shielding means 16 could take the form of a solidmetal member hermetically sealed to envelope 12 by suitable adhesivemeans. Shielding means 16 and 18, in addition to providing an electricalfunction, also serve as the means by which end cap assemblies 20 and 22,respectively, are hermetically sealed to envelope 12.

End cap assembly 20 comprises a ring 24 which adapts it to behermetically sealed to shielding means 16. Ring 24 has substantially thesame thermal coefficient or the same expansion characteristic asenvelope l2 and is compatible with shielding means 16 so as to beweldable thereto in a vacuumtight connection. In practice, ring 24 ismade of KOVAR metal alloy (iron-nickel-cobalt) or 52 nickel-balance ironor a similar alloy which has such thermal characteristics. In addition,ring 24 is cylindrical and is flared to a conic section to enhance itsexpandability and contractibility and area of adhesion. Ring 24 isbrazed to coating 16 on the exterior of envelope 12 by a suitablebrazing alloy or material such as gold (35 percent), copper (62 percent)and nickel (3 percent) heated to about l,025 C. or above. The specifiedalloy is compatible with KOVAR metal and with the nickel plate ofcoating 16 to form a physically strong hermetic seal.

End cap assembly 20 further comprises a cylindrical collar 26,preferably made of stainless steel having a low-carbon content toinhibit carbide precipitation during welding which could cause prematurefailure of the vacuum environment in envelope l2. Collar 26 is providedwith a shoulder 23 for automatically locating and spacing ring 24 andthe ring is fusion welded to the collar.

End cap assembly 20 also comprises an end plate 30 having a circulargroove 32 and a circular hole 34 for locating and spacing collar 26 andan electrical component such as a sta tionary contact stud 36,respectively, which is brazed thereto. Plate 30 serves as a meanswhereby electrical and mechanical connections are made to one end ofdevice l and also as a support means for an electrical component withinthe device. Plate 30 is also provided with a hole 38 for accommodating ametallic vacuum pinch-off tube ll) which has a shoulder 42 to facilitateits accurate location during brazing or welding.

Contact stud 36 is a cylindrical member of high purity copper and isprovided with a brazed on contact 44 made, for example, of tungsten,tungsten-copper or a copper alloy. Stud 36 is provided with a shoulder48 for locating it during braz ing. A supporting ring 50 is brazed orwelded to stud 3s and plate 30 to afford additional mechanical support.A disc-type arc shield 52, preferably of high-purity copper, is brazedor welded to stud 36.

The other end cap assembly 22 comprises a ring 54 and a collar 56similar to ring 24 and collar 26, hereinbefore described. However,collar 56 is further provided with an exterior shoulder 58 for locatinga mounting ring dill, preferably made of stainless steel, which iswelded thereto. Mounting ring 60 adapts device ill for physical mountingin a suitable environment. Collar 56 is also provided with an interiorshoulder 62 for locating a disc 64, preferably of copper, which isbrazed or welded thereto. Disc (i4 is provided with a central opening 66for accommodating a movable contact stud 68 and with a concentric groove70 for locating a cylindrical arc shield 72.

Arc shield 72 is a hollow cylindrical member or component made, forexample, of nickel, molybdenum or monel metal and is provided with aninterior shoulder 74- for locating a disc type arc shield 76 of the samematerial.

Movable contact stud 68 is a component similar to stud 3-16 hereinbeforedescribed and has a contact 78 thereon. Stud as is provided with anabutment or washer 3i), preferably of monel metal, to which one end ofacylindrical bellows r so of monel metal, is welded. The other end ofbellows 152. is brazed or welded to disc 64 at opening 66. Stud (nil isadapted for connection to an electrical conductor (not shown) and tomeans (not shown) which effect its axial movement to open and closedposition.

As is apparent from the foregoing description, device .14) is fabricatedof physically rugged, weather resistant materials which are capable ofsuperior electrical performance in outdoor use. From an electricalstandpoint, device ll ll has a high creepage to flashover length ratioto prevent external flashover and the high-vacuum interior also preventsflashover therein. Furthermore, the electrostatic shields lid and 18provide a unipotential interior to exterior seal area which minimizesundesirable corona effects and also provides a rugged hermetic seal forend cap assembly attachment. The parts of which device are made arestandardized geometric shapes which are readily fabricated from stockmaterials with simple machining operations. Furthermore, the parts arepremachined to interfit and permit automatic centering, distancing andalignment prior to brazing and/or welding. Materials are selected fromthe standpoint of corrosion resistance and compatibility to welding toadjacent components which may, of necessity, be of special materials.The total design and arrangement of all parts is such as to permitjigging and welding together of parts with a minimum number of brazingor welding operations.

The embodiments of the invention in which an exclusive property orprivilege we claim are defined as follows:

1. in a vacuum-type electrical device constructed to reduce voltagegradients therein and simplify manufacture,

a cylindrical envelope of ceramic insulating material having a cavitywherein a vacuum is maintained and arcing occurs,

said cavity having at least one opening communicating therewith which isdefined by a portion of said envelo which has an inside surface, an endsurface, and a con. exterior surface,

electrostatic shielding means comprising a metallic coating fused tosaid ceramic envelope on said conical exterior surface, on said endsurface and on a limited portion of said inside surface, an end capassembly for said opening, said end cap assembly comprising an annularmetal ring having a po: ion with a conical shape by which its insidesurface inn with and is brazed directly to said conical exterio velope,said ring having thermal expansion -i similar to those of said envelope,

and at least one electrically conductive contact stud connected to saidend cap assembly and extending cavity.

2. An electrical device according to claim l w cavity has a secondopening communicating there it in the same manner as said one opening,having second electrostatic shielding means similar to saidelectrostatic shiclu means for said one opening, and having a second endcap sembly which comprises a second annular metal ring similar to theaforesaid annular metal ring for said one end cap as sembly,

said second end cap assembly comprising a second collar sealed to saidsecond annular ring,

said second collar having an exterior and an interior shoulder,

a second mounting plate which is sealed against said enter or shoulderof said second collar,

a supporting disc which is sealed against said interior shoulder ofsaidsecond collar,

said supporting disc which is sealed against said interior shoulder ofsaid second collar,

said supporting disc having a central opening,

an electrically conductive second stud which extends through saidcentral opening in said disc,

an abutment disposed on said second stud,

and a cylindrical bellows sealed to said supporting disc and toabutment.

3. An electrical device according to claim 2 wherein said supportingdisc has a groove concentric with the central opening therein,

a hollow tubular arc shield which is aligned in said groove and sealedthereto,

said r' lindrical arc shield having a shoulder on the interior antadisc-type said tubular arc d. An electrical r coat. I nickel plated andicy.

5. An electrical device according to claim 1 whet-ch end cap assemblyfurther comprises collar sealed to said ring and a plate having analignment groove in wh sealed.

6. An electrical device according to claim wherein said collar has ashoulder against which said ring fits and is sealed.

'7. An electrical device according to claim 5 wh n said plate has acentral opening for accommodating and all ning said electricallyconductive stud which is sealed to said plate.

3. An electrical device according to claim 7 wherein sa d plate has anopening therein in which a pinch-off tube is sealer? and wherein saidstud is provided with a disc-type arc shield.

. rrio where a i d

1. In a vacuum-type electrical device constructed to reduce voltagegradients therein and simplify manufacture, a cylindrical envelope ofceramic insulating material having a cavity wherein a vacuum ismaintained and arcing occurs, said cavity having at least one openingcommunicating therewith which is defined by a portion of said envelopewhich has an inside surface, an end surface, and a conical exteriorsurface, electrostatic shielding means comprising a metallic coatingfused to said ceramic envelope on said conical exterior surface, on saidend surface and on a limited portion of said inside surface, an end capassembly for said opening, said end cap assembly comprising an annularmetal ring having a portion with a conical shape by which its insidesurface mates with and is brazed directly to said conical exteriorsurface on said envelope, said ring having thermal expansioncharacteristics similar to those of said envelope, and at least oneelectrically conductive contact stud connected to said end cap assemblyand extending into said cavity.
 2. An electrical device according toclaim 1 wherein said cavity has a second opening communicating therewithdefined in the same manner as said one opening, having secondelectrostatic shielding means similar to said electrostatic shieldingmeans for said one opening, and having a second end cap assembly whichcomprises a second annular metal ring similar to the aforesaid annularmetal ring for said one end cap assembly, said second end cap assemblycomprising a second collar sealed to said second annular ring, saidsecond collar having an exterior and an interior shoulder, a secondmounting plate which is sealed against said exterior shoulder of saidsecond collar, a supporting disc which is sealed against said interiorshoulder of said second collar, said supporting disc which is sealedagainst said interior shoulder of said second collar, said supportingdisc having a central opening, an eLectrically conductive second studwhich extends through said central opening in said disc, an abutmentdisposed on said second stud, and a cylindrical bellows sealed to saidsupporting disc and to said abutment.
 3. An electrical device accordingto claim 2 wherein said supporting disc has a groove concentric with thecentral opening therein, a hollow tubular arc shield which is aligned insaid groove and sealed thereto, said cylindrical arc shield having ashoulder on the interior thereof, and a disc-type arc shield sealedagainst said shoulder of said tubular arc shield.
 4. An electricaldevice according to claim 1 wherein said coating comprises amolybdenum-manganese alloy which is nickel plated and wherein said ringis an iron-nickel-cobalt alloy.
 5. An electrical device according toclaim 1 wherein said end cap assembly further comprises a collar sealedto said ring and a plate having an alignment groove in which said collaris sealed.
 6. An electrical device according to claim 5 wherein saidcollar has a shoulder against which said ring fits and is sealed.
 7. Anelectrical device according to claim 5 wherein said plate has a centralopening for accommodating and aligning said electrically conductive studwhich is sealed to said plate.
 8. An electrical device according toclaim 7 wherein said plate has an opening therein in which a pinch-offtube is sealed and wherein said stud is provided with a disc-type arcshield.